The present invention relates to a variable control of the gas exchange in internal combustion engines.
The term gas exchange describes the periodic change of the cylinder fill, i.e., the emission of exhaust gas and the intake of a fuel-air mixture. In conventional internal combustion engines, control of the gas exchange is effected via spring-loaded valves that are opened by a camshaft. The opening function as a time characteristic of the valve opening, i.e., beginning, duration and dimension of the opening cross-section, is determined by the shape of the camshaft. The opening function in conventional internal combustion engines can therefore be precisely determined by the shape of the camshaft, but is not variable. In addition, gas-exchange control systems are known that have a variable opening function. PCT Publication No. 91/08384 describes electromagnetically-controlled and hydraulically-actuated valves with a variable opening function. To eliminate the effects of tolerances and manifestations of aging in valve actuation, the valve lift is detected by a valve lift sensor, and the detected value is taken into consideration when triggering the valve. Here, the problem lies in allocating the valve lift sensor signal to the actual valve lift. For instance, the sensor signal can contain offsets that make a correct allocation difficult. To remedy this situation, the valve lift sensor described in PCT Publication No. 91/08384 is calibrated after each closing action. In the absence of a valve opening signal, the valve lift sensor signal is arbitrarily set to zero. This calibration is correct if the valve is actually closed, which is the case when actuation is intact and there is no opening signal. However, in cases where the valve does not close due to a malfunction, this calibration results in a false zero setting of the valve lift sensor.
German Published Patent Application No. 195 01 386 shows a variable valve control, where the opening function of the gas-exchange valves is determined by an opening camshaft and a closing camshaft. The opening function can be varied within a wide range by changing the phase shift between the shafts rotating at the same speed. The phase shift is changed via a linkage. With this system, a phase-angle sensor in the valve activation mechanism can detect the actual movement of the valves and/or the valve activation elements.
The problem here is that of coordinating the position of the phase-angle sensor with the position of the opening intake valves.
An object of the present invention is to improve the control of valves having variable valve lift.
This is achieved by a method for controlling a valve, having a variable valve lift, situated in an intake or exhaust opening of a combustion chamber of an internal combustion engine. With the method according to the present invention for controlling a valve having a variable valve lift, situated in an intake or exhaust opening of a combustion chamber of an internal combustion engine, the valve is controlled as a function of an analysis of a pressure in the combustion chamber. This is achieved in a particularly advantageous manner by a method for controlling a valve having a variable valve lift, situated in an intake or exhaust opening of a combustion chamber of an internal combustion engine, by providing valve lift sensor for supplying a lift signal indicating the position of the valve, with an automatic calibration of the valve lift sensor being carried out as a function of an analysis of a pressure in the combustion chamber. This makes it possible to automatically calibrate a valve lift sensor, such as a phase-angle sensor. An elaborate adjustment of the sensor (or phase angle sensor) during assembly is therefore no longer necessary. Furthermore, the automatic calibration lowers the requirements on the sensor tolerances.
The device according to the present invention for controlling a valve having a variable valve lift, situated in an intake or exhaust opening of a combustion chamber of an internal combustion engine, has a combustion chamber pressure sensor for providing a pressure signal indicating a pressure in the combustion chamber, a control device for controlling the valve lift, and an analyzer for analyzing the pressure signal.
A further device according to the present invention for controlling a valve having a variable valve lift, situated in an intake or exhaust opening of a combustion chamber of an internal combustion engine, has a valve lift sensor for providing a lift signal indicating the valve position, a combustion chamber pressure sensor for providing a pressure signal indicating a pressure in the combustion chamber, a control device for controlling the valve lift as a function of the lift signal, as well as an analyzer for analyzing the pressure signal and for calibrating the lift signal as a function of the analysis of the pressure signal.
A particular further advantage is the diagnosis of the intake valves to check for tight closing. This permits the early detection of beginning leaks such as can be caused by a valve clearance that is too small. Indication and/or storage of this error permits an early correction of the valve clearance, either through automatic intervention by the electronic valve control or by suitable maintenance measures. This can prevent expensive damage caused by burning of the valves due to insufficient heat dissipation via the valve seat.
In addition, the present invention not only permits adaptation and diagnosis of the intake-valve lift, but also of the exhaust-valve lift.
If, after an intake, the intake as well as the exhaust valves (i.e., the valves in the intake and exhaust openings) are completely closed, e.g., in coasting mode without ignition, the pressure in the combustion chamber approximately follows a steady sinusoidal course. Depending on the fill during the last intake, the pressure in the combustion chamber rises above the atmospheric pressure due to compression if the piston is in the uppermost position, and sinks below atmospheric pressure, if the piston is in the lowermost position. A deviation from this sinusoidal course, and especially a reduction of the maximum values, is advantageously interpreted as a beginning valve lift of either the intake valve or the exhaust valve. With the help of a test function, where a valve lift actuator for resetting a valve during coasting without ignition is steadily triggered from the neutral position in the direction of valve lift, an advantageous embodiment determines the zero position for the valve lift by detecting a deviation from the initial pressure characteristic.
Furthermore, in comparing the pressure curves to those of the above-mentioned test function, an incomplete sealing of the intake and/or exhaust valve can be detected. In a situation where the intake as well as the exhaust valve remain closed while the internal combustion engine keeps running (for instance during coasting without ignition), the advantages are seen as a correct closing if the pressure in the combustion chamber, as expected, again follows the aforementioned sinusoidal course with constant maximum values. If the pressure maximums, even without triggering the valve lift actuator, decrease gradually, and in a way where each maximum is smaller than the previous one, this is interpreted as a valve defect. If, on the other hand, for instance in the case of a tight intake valve which opens due to a beginning valve stroke, the pressure maximum only decreases with every other compression phase, this is advantageously interpreted as a valve opening.